Light scanning apparatus

ABSTRACT

Provided is a light scanning apparatus, including a light source, a light source controller to control an on/off operation of the light source, a light deflector deflecting light emitted from the light source, an image formation optical system to direct light deflected by the light deflector on a scan area of a to-be-scanned surface, a synchronous signal detector to receive the light emitted from the light source and to detect a synchronous signal for light scanning, and a light path changer changing a path of light emitted from the light source and incident upon the light deflector.

PRIORITY

This application is a continuation of U.S. patent application Ser. No.11/143,626, filed on Jun. 3, 205, and claims the benefit under 35 U.S.C.§ 119(a) of Korean Patent Application No. 2004-79962, filed on Oct. 7,2004, the entire disclosures of both of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light scanning apparatus for scanninglight emitted from a light source. More particularly, the presentinvention relates to a light scanning apparatus having a relativelycompact structure.

2. Description of the Related Art

Generally, light scanning apparatuses such as laser scanning units, areapplied to image forming apparatuses for printing an image on paper.Examples of image forming apparatuses include copiers, laser printers,and the like. In light scanning apparatuses, light emitted from a lightsource scans a photosensitive medium to form an electrostatic latentimage.

FIG. 1 is a construction diagram of an example of a conventional lightscanning apparatus. FIG. 2 illustrates an angle at which a beam of lightis incident upon a rotational multi-sided mirror 7.

Referring to FIG. 1, the conventional light scanning apparatus includesa light source 2 formed of a laser diode. A light source controllercontrols an on/off operation of the light source 2 and a collimatinglens 3 to convert divergent laser light emitted from the light source 2into parallel light or convergent light. The light source controlleralso controls a cylinder lens 5 for making laser light which passesthrough the collimating lens 3 to have a bar-shaped cross-section.Additionally, the light source controller controls the rotationalmulti-sided mirror 7 for deflecting laser light, an f-θ lens 9 disposedbetween the rotational multi-sided mirror 7 and a to-be-scanned surface20, a reflection mirror 11 reflecting laser light for use in synchronoussignal detection, a synchronous signal detection lens 13 collecting thelaser light reflected by the reflection mirror 11, and a photodetector15 to receive laser light for use in synchronous signal detection. Thelight source controller is comprised of a semiconductor device installedon a circuit board 1 and a control circuit formed in a predeterminedpattern. The light source 2 and the photodetector 15 are generallyinstalled on the circuit board 1 in order to minimize the size of thelight scanning apparatus and to reduce manufacturing costs.

Referring to FIG. 2, laser light beam Al is incident upon the rotationalmulti-sided mirror 7 at an angle θ₁ with a normal line N₁ of a mirrorside 7 a. The rotational multi-sided mirror 7 is hexagonal. A length L₁of each side of the rotational multi-sided mirror 7 is proportional tothe incidence angle θ₁. Thus, as the incidence angle θ₁ increases, thelength L₁ of each side of the rotational multi-sided mirror 7 increases.Consequently, the rotational multi-sided mirror 7 is enlarged. Enlargingthe rotational multi-sided mirror 7 leads to increased costs formanufacturing the light scanning apparatus. Also, noise generated due torotation of the rotational multi-sided mirror 7 is increased.

As shown in FIG. 1, in order to solve the above-described problems, thelight source 2 and the circuit board 1 may be disposed so that a lightbeam is incident upon the rotational multi-sided mirror 7 at an angle tothe to-be-scanned surface 20 instead of being parallel thereto. However,in this case, the photodetector 15 is rendered aslant. Consequently, thelaser light used in synchronous signal detection is incident aslant upona light receiving surface of the photodetector 15. Consequently, thereliability of synchronous signal detection degrades.

Accordingly, there is a need for a light scanning apparatus in whichlight is incident upon a side of a rotational multi-sided mirror at anangle smaller than that in a conventional light scanning apparatus.

SUMMARY OF THE INVENTION

An aspect of the present invention is to solve at least the aboveproblems and/or disadvantages and to provide at least the advantagesdescribed below. Accordingly, an aspect of the present invention is toprovide a light scanning apparatus in which light is incident upon aside of a rotational multi-sided mirror at an angle smaller than that ina conventional light scanning apparatus so that the rotationalmulti-sided mirror is minimized in size.

Another aspect of the invention is to provide a light scanning apparatusin which a synchronous signal is more reliably detected.

According to an yet another aspect of the present invention, there isprovided a light scanning apparatus which comprises a light source, alight source controller for controlling on/off operation of the lightsource, a light deflector to deflect light emitted from the lightsource, and an image formation optical system to direct light deflectedby the light deflector on a scan area of a to-be-scanned surface.Additionally, a synchronous signal detector to receive the light emittedfrom the light source and detecting a synchronous signal for lightscanning is disclosed. A light path changer to change a path of lightemitted from the light source is provided to incident light upon thelight deflector.

It is also preferable that the light path changer include a firstreflection mirror to reflect light emitted from the light source.Moreover, the light path changer may also include a second reflectionmirror which re-reflects the light reflected by the first reflectionmirror so that the re-reflected light advances toward the lightdeflector.

It is also preferable that a rectilinear line extending in a directionof the light emitted from the light source may not be parallel to arectilinear line extending in a direction of the light incident upon thelight deflector.

It is still preferable that the light source controller include acircuit board and a control circuit formed on the circuit board to havea predetermined pattern. The synchronous signal detector may include aphotodetector that receives light and converts the light into asynchronous signal. The photodetector may be mounted on the circuitboard of the light source controller.

An incidence angle made by a rectilinear line preferably extends in adirection of light incident upon a light-receiving surface of thephotodetector and a normal line perpendicular to a light-receivingsurface of the photodetector may be about 0 degrees.

The rectilinear line extending in the direction of the light emittedfrom the light source may be substantially parallel to the rectilinearline extending in the direction of light incident upon a light-receivingsurface of the photodetector.

The light scanning apparatus may further include a collimating lenswhich converts the light emitted from the light source into parallellight or convergent light, and a cylinder lens which transforms thelight passed through collimating lens so that a cross-section of thelight is in a bar shape. The light path changer may be disposed betweenthe cylinder lens and the light deflector so as to change a path oflight passed through the cylinder lens.

Other objects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of certainembodiments of the present invention will be more apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which;

FIG. 1 is a construction diagram of an example of a conventional lightscanning apparatus;

FIG. 2 illustrates an angle at which light is incident upon a rotationalmulti-sided mirror of FIG. 1;

FIG. 3 is a construction diagram of a light scanning apparatus inaccordance with an exemplary embodiment of the present invention;

FIG. 4 illustrates the light incidence angle of FIG. 2 and an angle atwhich light is incident upon a rotational multi-sided mirror of FIG. 3;and

FIG. 5 illustrates angles at which light is incident upon photodetectorsof a conventional light scanning apparatus and the light scanningapparatus of FIG. 3.

Throughout the drawings, the same drawing reference numerals will beunderstood to refer to the same elements, features, and structures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The matters defined in the description such as a detailed constructionand elements are provided to assist in a comprehensive understanding ofthe embodiments of the invention. Accordingly, those of ordinary skillin the art will recognize that various changes and modifications of theembodiments described herein can be made without departing from thescope and spirit of the invention. Also, descriptions of well-knownfunctions and constructions are omitted for clarity and conciseness.

FIG. 3 is a construction diagram of a light scanning apparatus 100according to an exemplary embodiment of the present invention. FIG. 4illustrates a light incidence angle of FIG. 2 and an angle at whichlight is incident upon a rotational multi-sided mirror 130 of FIG. 3.FIG. 5 illustrates angles at which light is incident upon aphotodetector of a conventional light scanning apparatus and aphotodetector 150 of FIG. 3.

Referring to FIG. 3, the light scanning apparatus 100 includes a lightsource 110, a light deflector, an image formation optical system, asynchronous signal detector, a light source controller, a collimatinglens 115, and a cylinder lens 117. The light source 110 emits lightaccording to an image signal. The light deflector includes therotational multi-sided mirror 130 to deflect light emitted from thelight source 10. The image formation optical system forms an image on ato-be-scanned surface 160. For example, an image is formed on animage-forming surface of a photosensitive medium of an image formingapparatus by scanning the to-be-scanned surface 160 with light deflectedby the light deflector. The synchronous signal detector detects asynchronous signal for horizontal synchronization using part of thelight deflected by the light deflector. The light source controllercontrols an on/off operation of the light source 110 according to theimage signal. The collimating lens 115 converts divergent light emittedfrom the light source 110 into parallel light or convergent light. Thecylinder lens 117 transmits the light which passes through thecollimating lens 115. Thus, the light is directed linearly on a surfaceof the rotational multi-sided mirror 130. The cylinder lens 117 hasdifferent refraction rates in a main scan direction parallel to an axisX and a sub-scan direction parallel to an axis Z, which is perpendicularto axes X and Y. Thus, the cylinder lens 117 can direct light on asurface of the rotational multi-sided mirror 130 linearly in the mainscan direction.

The light source 110 may be formed of a single light source or aplurality of light sources. Each light source has either a singlelight-emitting point or a plurality of light-emitting points.Preferably, a laser diode is used as the light source 110 to emit laserlight.

The light source controller includes a circuit board 105 and a controlcircuit formed on the circuit board 105 to have a predetermined pattern.The light source 110 is mounted on the circuit board 105. Light emittedfrom the light source 110 advances in a direction substantially parallelto the axis X via the collimating lens 115. The term “substantially”means that a slight error may be allowed due to a factor, such as atechnical limit or the like.

To set a traveling direction of the light emitted from the light source110 to be parallel to the axis X, the circuit board 105 is located on aplane substantially parallel to a plane including the axes Y and Z(i.e., a Y-Z plane).

The light deflector projects light at an equi-linear speed in ahorizontal direction. That is, the main scan direction, and includes therotational multi-sided mirror 130. The multi-sided mirror is preferablyhexagonal. The light deflector also includes a driving source (notshown), such as a motor for rotating the rotational multi-sided mirror130. Referring to FIG. 3, the rotational multi-sided mirror 130 isrotated at a constant speed in one direction by the driving sourceduring image formation and has a plurality of sides 130 a.

The image formation optical system forms an image on the to-be-scannedsurface 160. For example, the image formation optical system forms animage-forming surface of a photosensitive medium by correcting anaberration of light deflected by the side 130 a of the rotationalmulti-sided mirror 130. The image formation optical system is formed ofone or more optical components including an f-θ lens 135. The f-θ lens135 advances light deflected by the side 130 a of the rotationalmulti-sided mirror 130 in the main scan direction and the sub-scandirection with different refraction rates so that an image is formed onthe to-be-scanned surface 160.

The synchronous signal detector includes a third reflection mirror 140for changing a travel path of light for synchronous signal detectiondeflected by the rotational multi-sided mirror 130. The synchronoussignal detector also includes a synchronous signal detection lens 145for focusing light reflected by the third reflection mirror 140 and aphotodetector 150 to receive the light for synchronous signal detectionfocused by the synchronous signal detection lens 145. The light forsynchronous signal detection reflected by the third reflection mirror140 travels substantially parallel to the axis X, like the light emittedfrom the light source 110. Then, the light sequentially passes throughthe collimating lens 115 and the cylinder lens 117. The synchronoussignal detection lens 145 directs the light for synchronous signaldetection on a light-receiving surface 150 a (see FIG. 5) of thephotodetector 150. The photodetector 150 receives the light forsynchronous signal detection and converts the same into a synchronoussignal for horizontal synchronization. The photodetector 150 is mountedon the circuit board 105, which is included in the light sourcecontroller.

The light scanning apparatus 100 includes a light path changer forchanging a path of light emitted from the light source 110 and incidentupon the rotational multi-sided mirror 130 of the light deflector. Morespecifically, the light path changer is located between the cylinderlens 117 and the rotational multi-sided mirror 130 so as to change apath of light transmitted through the cylinder lens 117. The light pathchanger includes first and second reflection mirrors 120 and 125. Thefirst reflection mirror 120 reflects light emitted from the light source110 that passes through the cylinder lens 117. The second reflectionmirror 125 re-reflects light reflected by the first reflection mirror120 so that the re-reflected light is incident upon the rotationalmulti-sided mirror 130. The light emitted from the light source 110sequentially passes through the collimating lens 115. The cylinder lens117 is not parallel to the light incident upon the rotationalmulti-sided mirror 130 which is reflected by the second reflectionmirror 125.

Referring to FIG. 4, an angle θ₂ at which light is incident upon theside 130 a of the rotational multi-sided mirror 130 may be smaller thanan angle θ₁ in a conventional light scanning apparatus. This is due tothe change of the light path by the first and second reflection mirrors120 and 125. More specifically, the angle θ₂ in the light scanningapparatus 100 is smaller than the angle θ₁in the conventional lightscanning apparatus when a rotating multi-sided mirror in theconventional light scanning apparatus and the rotational multi-sidedmirror 130 are rotated and located at an identical position. Referencecharacters A₁ and A₂ denote a direction of incident light in theconventional light scanning apparatus and a direction of incident lightin the light scanning apparatus 100, respectively. Reference characterN₁ denotes a normal line perpendicular to the side 130 a.

Referring to FIG. 5, the photodetector 150 mounted on the circuit board105 of FIG. 3 is disposed so that an angle θ₄ made by a rectilinear lineA₃ extends in a direction of light incident upon the light-receivingsurface 150 a and a normal line perpendicular to the light-receivingsurface 150 a is about 0 degrees. On the other hand, in a conventionalapparatus, although a traveling direction of light incident upon aphotodetector is the same as the direction of the light incident uponthe light-receiving surface 150 a of the photodetector 150 in thepresent embodiment, a normal line N₂ perpendicular to thelight-receiving surface 150 a of the photodetector 150 is at an angle incontrast with the present invention. Hence, an incidence angle θ₃ madeby the rectilinear line A₃ extending in the direction of the lightincident upon the light-receiving surface 150 a and the normal line N₂is about no less than 0 and no more than 90.

A light scanning apparatus in accordance with embodiments of the presentinvention has the following effects. First, an angle at which light isincident upon a light deflector may be reduced compared withconventional apparatuses. Accordingly, the light deflector can beminimized, costs for manufacturing the light scanning apparatus may belowered, and noise generated upon light scanning may be reduced.

Second, an angle at which light for synchronous signal detection isincident upon a photodetector may be set to substantially about 0degrees. Thus, the drawbacks of the synchronous signal detection may bereduced compared with conventional apparatuses.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A light scanning apparatus comprising: a light source; a lightdeflector deflecting light emitted from the light source; an imageformation optical system to direct light deflected by the lightdeflector on a scan area of a surface to be scanned; a light pathchanger disposed between said light source and said light deflector tochange a path of the light emitted from the light source and incidentupon the light deflector, wherein an incident angle of a light reflectedby said light path changer with respect to said light deflector issmaller than an incident angle of a direct light from said light sourcewith respect to said light deflector.
 2. The light scanning apparatus ofclaim 1, wherein the light path changer comprises at least two mirrors.3. The light scanning apparatus of claim 1, further comprising: a lightdetector that receives the light emitted from the light source andconverts the light into a synchronous signal; wherein the light detectorand the light source are installed on the same surface and the lightemitted from the light source is substantially parallel to the lightincident upon a light-receiving surface of the light detector.